SATCOM SYSTEM -SATELLITE DATA UNIT FUNCTIONAL DESCRIPTION
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Airplane identification number and digital communication data (data communication management function (DCMF) bus from left and right AIMS cabinets)
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Time and date (general purpose (GP) 1 bus from left AIMS cabinet)
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Data load data (data load bus from the left AIMS cabinet)
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Data load discrete (from the left AIMS cabinet)
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Control and BITE signals (central maintenance computer (CMC) bus from the left AIMS cabinet).
The SDU sends the following data to the AIMS cabinets:
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SDU status and BITE data (CMC bus to both left and right AIMS cabinets)
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Data load data (data load bus to left AIMS cabinet)
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Digital communication data (data communication management function (DCMF) bus to both left and right AIMS cabinets).
The SDU also sends and gets BITE and control data from these units:
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RFU
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High power amplifiers (HPAs)
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Beam steering units (BSUs).
Audio Interface
The audio interface connects the SDU to the audio management unit (AMU). It changes analog audio from the AMU to digital data for the SDU. It also changes the digital SDU data to analog voice signals for the AMU.
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System Processor
The system processor controls all operations of the satellite data unit and operates the complete SATCOM system. It sends call lights signals to the AMU. The memory keeps data for:
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System operation
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Satellite identification
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Ground station identification
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Channel frequencies.
The systems processor sends control signals to the low gain system low noise amplifier/diplexer (LNA/DIP). It also receives BITE data from the LNA/DIP.
You use switch inputs from the front panel to make the processor start a test of the SDU. The processor sends display data to the front panel to show the status of the test.
2016 MHz Phase Locked Oscillator
The 2016 MHz oscillator gets its input from a 10.08 MHz precision oscillator. The 2016 MHz goes to the converters to change the input and output frequencies. It also gets mixed with the RF output for the RFU to use as a reference.
10.08 MHz Precision Oscillator
The SATCOM system uses this oscillator as a precise reference for the modulation and demodulation of the RF signals. The SDU also uses it as its base reference frequency for the processor.
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SATCOM SYSTEM -SATELLITE DATA UNIT FUNCTIONAL DESCRIPTION
Passenger Telephone Interface
The SDU gets inputs from the cabin telecommunication unit (CTU) for the passenger telephone system. The SDU sends the signals directly to the RFU.
Facsimile
This interface connects the SDU to the facsimile machine (FAX) for the passenger telephone system. The FAX sends data signals to the SDU. The SDU sends the data signals to the RFU. The RFU sends received facsimile information to the SDU. The SDU sends the data signals to the FAX machine.
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SATCOM SYSTEM -RADIO FREQUENCY UNIT FUNCTIONAL DESCRIPTION
General
The radio frequency unit (RFU) changes digital audio from the cabin telecommunications unit (CTU) and satellite data unit (SDU) to radio frequency (RF) signals. The RFU has three voice/ data channels. If the passenger telephone system needs to use more than three channels, the RFU passes the digital audio to the SDU. The SDU supplies two additional voice channels.
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